> For the complete documentation index, see [llms.txt](https://docs.lorric.com/qr/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.lorric.com/qr/fp-as310-paddle-wheel-flowmeter-manual-chinese-v1/communication/modbus-rtu-protocol.md).

# Modbus RTU Protocol

## 通訊格式

bit order: lsb first

byte order: big endian

Data bits:8 

Parity: None 

Stop bits: 1

Floating point number follows IEEE754-1985. The float32 below stands for 32bits Single precision floating point number.

## 名詞定義

Register: 2 Byte 或 16bit 長，是 Modbus RTU 的記憶體通訊的單位長度。

Byte: 8 bit長

## 記憶體定義及功能

modbus 可操作的記憶體分為兩大類，唯讀型及讀寫型。

唯讀型主要是流量計狀態相關的記憶體，例如即時流量。這部分也是最常使用的記憶體。唯讀型的記憶體只能使用指 04 來讀取。相關頁面如下：

{% content-ref url="/pages/-LxsVE58yaYDg\_hQIiDw" %}
[唯讀型記憶體讀取指令(04)及記憶體列表](/qr/fp-as310-paddle-wheel-flowmeter-manual-chinese-v1/communication/modbus-rtu-protocol/wei-du-xing-ji-yi-ti/read-only-memory-read-instruction-04-and-memory-lists.md)
{% endcontent-ref %}

FP-AS310R 只支援使用 01/05 指令將累計流量歸零。


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